1. Field of the Invention
The invention relates to a rotary drive assembly for a drill rod having an outer tube and an inner rod extending at least in sections inside the outer tube, in particular for double-head and/or superposed drilling.
2. Related Art
A rotary drive assembly of such type includes a first gear unit having at least a first drive unit for driving the inner rod in a rotating manner and at least a second gear unit, which is arranged offset to the said first gear unit in the longitudinal direction of the drill rod and has at least a second drive unit for driving the outer tube in a rotating manner.
Rotary drive assemblies for double-head drilling devices are known that have two gear units arranged one behind the other in the longitudinal direction of the drill rod, in which case one of the gear units serves for the rotating operation of the inner rod while the other serves for the rotating operation of the outer tube of the drill rod. To drive the two gear units a hydraulic drive unit is each mounted on the two associated gear housings, with the drive shaft of each gear unit being directly connected to the associated drive unit.
However, such drive assemblies can have a comparatively large constructional length in the direction of the drill rod, that results from the sum of the constructional lengths of both gear units as well as both drive units. With a view to achieving a length of utilization as large as possible, i.e. an insertion depth of the drill rod, a constructional length as short as possible is generally to be aimed for.
Further rotary drive assemblies are known from DE 197 04 263 C1 and DE 100 05 475 A1. These drive assemblies have a common drive unit, the torque of which is distributed upon a different rotational direction both to the outer tube and to the inner rod. In these known assemblies there usually exists a forced synchronization of the rotational speed of the outer tube with the rotational speed of the inner rod.